Mid-arm torsion spring in a switchable roller finger follower

ABSTRACT

A compact switchable roller finger follower having an inner arm and outer arm for a Type II valve train is described. The compact switchable roller finger follower has its widest portion at a mid-arm position. One or more torsion springs provide a restoring force to urge the inner arm into a nested position in the upper arm in which position the inner arm may be locked to the outer arm so that a cam lobe profile is transferred into valve motion. At least one of the torsion springs is located at a mid-arm position.

FIELD OF THE INVENTION

The described embodiments relate generally to a compact switchable roller finger follower having an inner arm and outer arm for a Type II valve train. The compact switchable roller finger follower has its widest portion at a mid-arm position.

BACKGROUND

The output of many internal combustion engines is controlled by adjusting the mass air charge (MAC) delivered to each fired cylinder. An engine control unit (ECU) directs delivery of the appropriate fuel charge for the commanded MAC. Gasoline fueled engines generally operate with an air/fuel ratio at or near stoichiometry to facilitate conversion of harmful pollutants to more benign compounds in a catalytic converter. Control of the MAC is most easily accomplished by adjusting the throttle position which in turn alters the intake manifold pressure (MAP). However, it should be appreciated that the MAC can be varied using other techniques as well. For example, variable intake valve lift control can be used to adjust the MAC. Adjusting the valve lift has the advantage of reducing pumping losses thereby increasing fuel efficiency, particularly at low or intermediate engine loads.

Over the years there have been a wide variety of efforts made to improve the fuel efficiency and reduce the noxious emissions of internal combustion engines. One approach that has gained popularity is to vary the displacement of the engine. Most commercially available variable displacement engines effectively “shut down” or “deactivate” some of the cylinders during certain low-load operating conditions. When a cylinder is “deactivated”, its piston typically still reciprocates; however, neither air nor fuel is delivered to the cylinder so the piston does not deliver any net power. Since the cylinders that are shut down do not deliver any power, the proportional load on the remaining cylinders is increased, thereby allowing the remaining cylinders to operate with improved fuel efficiency. Also, the reduction in pumping losses improves overall engine efficiency resulting in further improved fuel efficiency. Variable displacement operation allows better control over the temperature of the combustion exhaust gasses, which can improve the efficacy of an aftertreatment system that reduces noxious emissions.

Another method of controlling internal combustion engines is skip fire control where selected combustion events are skipped during operation of an internal combustion engine so that other working cycles operate at better efficiency. In general, skip fire engine control contemplates selectively skipping the firing of certain cylinders during selected firing opportunities. Thus, for example, a particular cylinder may be fired during one firing opportunity and then may be skipped during the next firing opportunity and then selectively skipped or fired during the next. This is contrasted with conventional variable displacement engine operation in which a fixed set of the cylinders are deactivated during certain low-load operating conditions. In a conventional variable displacement engine the sequence of specific cylinders' firings will always be the same for each engine cycle during operation in a variable displacement mode (so long as the engine remains in the same displacement mode), whereas that is often not the case during skip fire operation. For example, an 8-cylinder skip fire controlled engine operating at a firing fraction of ⅓ will have different patterns of fired and skipped cylinders on successive engine cycles. Skipped cylinders are also preferably deactivated during skipped working cycles in the sense that air is not pumped through the cylinder and no fuel is delivered and/or combusted during skipped working cycles when such valve deactivation mechanism is available. Often, no air is introduced to the deactivated cylinders during the skipped working cycles thereby reducing pumping losses. The Applicant has filed a number of patent applications generally directed at dynamic skip fire control. These include U.S. Pat. Nos. 7,849,835; 7,886,715; 7,954,474; 8,099,224; 8,131,445; 8,131,447; 8,336,521; 8,449,743; 8,511,281; 8,616,181; 8,839,766: 9,086,020 9,689,327; 9,512,794; and 10,247,072.

One known method to enable cylinder deactivation is to use a Type II valve train with a switchable roller finger follower (RFF). With the valve train hardware currently available, adding a switchable RFF to the valve train to enable cylinder deactivation may require extensive redesign of the valvetrain and cylinder head to accommodate the extra size of a switchable RFF as compared to a non-switchable RFF. There is a need for a more compact switchable RFF that can more easily be integrated into existing engine designs.

SUMMARY

A compact switchable roller finger follower having an inner arm and outer arm for a Type II valve train is described. The compact switchable roller finger follower has its widest portion at a mid-arm position. One or more torsion springs provide a restoring force to urge the inner arm into a nested position in the upper arm in which position the inner arm may be locked to the outer arm so that a cam lobe profile is transferred into valve motion. At least one of the torsion springs is located at a mid-arm position.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which:

FIG. 1 shows a portion of a prior art Type II valve train.

FIG. 2A is a perspective view of a prior art switchable roller finger follower having a torsion spring located on a lash adjuster end of the switchable roller finger follower.

FIG. 2B is a cross-sectional view of a prior art switchable roller finger follower having a torsion spring located on a valve end of the switchable roller finger follower.

FIG. 3 shows a top perspective view of a compact switchable roller finger follower according to an embodiment of the current invention.

FIG. 4 shows a bottom perspective view of a compact switchable roller finger follower according to an embodiment of the current invention.

FIG. 5 shows a side perspective view of a compact switchable roller finger follower according to an embodiment of the current invention.

FIG. 6 shows a perspective view of an outer arm according to an embodiment of the current invention.

FIG. 7 shows a perspective view of an inner arm according to an embodiment of the current invention.

FIG. 8 shows a top view of a compact switchable roller finger follower according to an embodiment of the current invention.

In the drawings, like reference numerals are sometimes used to designate like structural elements. It should also be appreciated that the depictions in the figures are diagrammatic and not to scale.

DETAILED DESCRIPTION

In this patent application, numerous specific details are set forth to provide a thorough understanding of the concepts underlying the described embodiments. It will be apparent, however, to one skilled in the art that the described embodiments may be practiced without some or all of these specific details. In other instances, well known mechanical elements have not been described in detail in order to avoid unnecessarily obscuring the underlying concepts.

The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.

While the embodiments have been described in terms of particular embodiments, there are alterations, permutations, and equivalents, which fall within the scope of these general concepts. It should also be noted that there are alternative ways of implementing the methods and apparatuses of the present embodiments. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the described embodiments.

FIG. 1 shows a prior art Type II valve configuration used to control an intake or exhaust valve of an internal combustion engine. A Type II valve train utilizes an overhead camshaft 40 with the cam lobe profile 55 transferred to valve motion using a roller finger follower (RFF) 10. One end of the roller finger follower 10 pivots, typically on a hydraulic lash adjuster 21, and the opposed end of the RFF 21 contacts the valve 50. A cam follower 15 is situated midway between the two ends of the RFF 10. The valve 50 is forced upward by a valve spring 53. The valve 50 moves up and down alternating sealing (up position) and allowing gas to flow into or out of (down position) a cylinder in the internal combustion engine. The valve motion follows a lift profile, depicted by curve 45. Valve 50 motion is caused by rotation of a camshaft 40. The camshaft has a cam lobe 55, which rotates with the camshaft. The cam lobe 55 forces the RFF 10 to rotate downward when the portion of the cam lobe 55 extending from the base circle 57 contacts the roller finger follower (RFF) 10. The RFF 10 pivots about pivot point 25, which is formed at the contact area between the hydraulic lash adjuster (HLA) 21 and the RFF 10. Pressurized oil flows into the HLA 21 and upward thru the HLA to the pivot point 25. An oil passage (not shown in FIG. 1) passes through the pivot point 25 into the RFF 10, supplying oil to the RFF 10 to reduce friction and wear. The HLA 21 includes an internal mechanism that uses the pressurized oil to force the top of the HLA 21 against the RFF 10 reducing or eliminating any lash in the mechanical system. This reduces wear and valve train noise.

The basic Type II valve configuration is shown in FIG. 1 can be adapted for cylinder deactivation by using a switchable RFF. An example of a prior art switchable RFF 200 may be found in U.S. Pat. No. 10,294,834 and is shown in FIG. 2A. The switchable RFF 200 may have an outer arm 202 with an inner arm 204 pivotably connected to the outer arm near one end of the switchable RFF by a pivot shaft 206. A locking mechanism (not shown in FIG. 2A) either allows the inner arm 204 to pivot with respect to the outer arm 202 or locks the two together. A cam follower 208 tracks the profile of a rotating cam lobe (not shown in FIG. 2A). As the cam lobe rotates the cam follower 208 and thus inner arm 204 are pressed downward as the cam lobe profile 55 rises above the base circle 57 (se FIG. 1). If the inner arm 204 is locked to the outer arm 202, the entire switchable RFF 200 pivots about the end of the RFF above the hydraulic lash adjuster 21. If the inner arm 204 is unlocked, then only the inner arm 204 rotates downward in response to the cam lobe 55, and the outer arm 202 remains fixed. The switchable RFF 200 can be switched between its locked and unlocked position by applying pressurized hydraulic fluid, such as pressurized motor oil, to the switchable RFF. A first torsion spring 210 and second torsion spring 212 are located at the end of the switchable RFF 200 above the hydraulic lash adjuster 21. The first torsion spring 210 is located on one side of the switchable RFF 200 and the second torsion spring 212 is located on the opposite side of the switchable RFF 200. Both the first and second torsion springs 210 and 212 cooperate to urge the cam follower 208 and inner arm 204 upward against the cam lobe 55 profile if the inner arm 204 is unlocked. The locking mechanism can be engaged or disengage at any point on the cam lobe where the profile matches the base circle. Once the cam follower 208 comes off the base circle 57 the locking mechanism cannot be switched.

In other prior art switchable RFFs 240, the first torsion spring and second torsion spring are located at a valve end of the switchable RFF 240. An example of such a prior art switchable RFF 240 may be found in U.S. patent application No. 20070039573 and is shown in FIG. 2B. FIG. 2B is a cross-sectional view of a prior art switchable RFF 240. The general arrangement of the switchable RFF 240 is similar to that shown in FIG. 2A, but the position of the first torsion spring 210 has shifted. The first torsion spring is located at the valve end of the switchable RFF 240, not the HLA end as in FIG. 2A. The switchable RFF 240 has a second torsion spring 212 on the opposite side of the switchable RFF 240, which is not shown in this cross-sectional view.

A disadvantage with the prior art switchable RFFs 200 and 240 is that the first and second torsion springs 210 and 212 increase the width of the switchable RFF 200. It is particularly undesirable that the width of the switchable RFF is increased at an end of the switchable RFF, either at the lash adjuster end, FIG. 2A, or valve end, FIG. 2B. Many prior art valve train designs have other components in this region and redesigning the valvetrain and cylinder head to accommodate the increased width of the switchable RFF is difficult and expensive. There is a need for a more compact switchable RFF that can more easily be integrated into existing engine designs.

FIG. 3 shows a top perspective view and FIG. 4 shows a bottom perspective view of a compact switchable roller finger follower (RFF) 300 according to an embodiment of the current invention. In both the figures, the switchable RFF is shown with the inner arm nested into the outer arm, which is its position if the switchable RFF is locked or the cam follower is against the base circle. The compact switchable RFF 300 has a pair of torsion springs, a first torsion spring 310 and a second torsion spring 312 situated on opposing sides of an outer arm 302. A retainer 316 may help secure the first torsion spring 310 to a boss (not shown in FIG. 3 or 4) on the outer arm 302. The retainer 316 may be a circular disc press fit over the boss or may be a spring or clip. More generally the retainer 316 is any element that secures the first and second torsion springs 310 and 312 to the outer arm. A similar retention system may be used for both the first and second torsion springs 310 and 312. A lower end of the first torsion spring 310 and second torsion spring 312 may register against a Z-stop pin 314. The Z-stop pin 314 mechanically links the first torsion spring 310 with the second torsion spring 312 and the inner arm 304. The Z-stop pin 314 facilitates cooperative action of the first torsion spring 310 with the second torsion spring 312. Both the first and second torsion springs 310 and 312 cooperate to urge the cam follower 308 and inner arm 304 upward against the cam lobe 55 profile if the inner arm 304 is unlocked. The first and second torsion springs 310 and 312 also cooperate to reduce the risk of hydraulic lash adjuster pump-up. An upper end of the first torsion spring 310 and the second torsion spring 312 may register against a top surface of the outer arm. Other registration points for the upper and lower ends of the first torsion spring 310 and the second torsion spring 312 are possible.

A major difference between the prior art switchable roller finger followers 200 and 240 and the compact switchable roller finger follower 300 is the number and placement of torsion springs that press the inner arm against the cam lobe when the switchable RFF is unlocked. Prior art switchable roller finger followers have two torsion springs positioned outside the outer arm at one end of the outer arm. The prior art torsion springs may be positioned either adjacent the hydraulic lash adjuster 21, as shown in FIG. 2A, or the valve 50, as shown in FIG. 2B. Neither location is desirable because of interference issues with other valvetrain and cylinder head components. Having heavy springs over the valve is also undesirable, since the extra mass at this location may compromise valve performance at high speed dynamic engine operation. In the compact switchable RFF 300 a first torsion spring 310 and a second torsion spring 312 have been moved to a mid-arm position on an outer arm 302. In this position they do not interfere with other hardware that may be present near the hydraulic lash adjuster or valve.

FIG. 5 shows the compact switchable RFF 300 in an unlocked position with the inner arm 304 fully rotated by the peak of the cam lift profile (cam not shown in FIG. 5). The inner arm 304 is rotated downward about a pivot shaft 306 in response to a cam follower 308 tracking a cam lobe off the base circle 57. The first torsion spring 310 and second torsion spring 312 will more tightly coil as the Z-stop pin 314 forces a lower end of the torsion springs downward. The Z-stop pin 314 may be positioned within two holes in the inner arm 304. As the cam lobe moves past its peak, the first torsion spring 310 and second torsion spring 312 will push the Z-stop pin 314 upward until the inner arm 304 until it returns to its locked position, shown in FIGS. 3 and 4. In the locked position, the Z-stop pin may rest against the bottom of the outer arm 302.

An optional third torsion spring 318 is shown in FIGS. 3 and 5. The third torsion spring may to positioned over the pivot shaft 306. This space is normally available and not used for a torsion spring, so adding a third torsion spring is an effective use of the available space. Together the first, second, and optional third torsion springs 310, 312 and 318 provide sufficient force to urge the inner arm 304 upward into the outer arm 302 so that it may be locked into a nested position by a locking pin. By having a third torsion spring 318 the size and mass of the mid-arm mounted torsion springs 310 and 312 may be decreased. This may allow a reduction in the maximum width of the compact switchable RFF 300.

FIG. 6 shows an outer arm 302 of a compact switchable RFF 300 according to an embodiment of the current invention. The outer arm may have two bosses 320 located at a mid-arm position that extend outward from the outer arm 302 body. One boss is located on each side of the outer arm. Each boss provides a mounting surface for the coil of one of the mid-arm torsion springs 310 and 312. While the bosses 320 shown in FIG. 6 are shown integral to the outer arm body, this is not necessarily the case. One or both of the bosses 320 may be a separate element, which is permanently attached or affixed to the outer arm body. In independent of whether the boss is integral to the outer arm 302 or affixed to the outer arm 302, the outer arm 302 has two bosses that extend outward from the outer arm body at a mid-arm position.

FIG. 7 shows an inner arm 304 of a compact switchable RFF 300 according to an embodiment of the current invention. The inner arm 304 has two holes 322 that are situated on opposite sides of the inner arm. The holes 322 may be configured to accept a Z-stop pin 314 as shown in FIG. 5.

FIG. 8 shows a top view of a compact switchable RFF 300 according to an embodiment of the current invention. As is evident from FIG. 8 the widest portion of the compact switchable RFF is located at a mid-arm location. In this context, a mid-arm location refers to a position along the central half of length of the compact switchable RFF between the valve contact point and the lash adjuster contact point. That is a position between ¼ to ¾ of the length between the HLA contact position and the valve contact position. The mid-arm region 800 is illustrated in FIG. 8. By having the widest portion of the compact switchable RFF 300 in the mid-arm region, the free space adjacent the hydraulic lash adjuster and the valve is increased, which allows room in these regions for other valvetrain and cylinder head components. A torsion spring, or boss on which the torsion spring is supported, may be considered to be located at a mid-arm position if the center of the boss or torsion spring coil is within the central half of the length of the compact switchable RFF 300.

In alternative embodiments, the first and second torsion spring and the Z-stop pin may be replaced by a single torsion spring. The spring would have two coiled sections that would be situated on both sides of the outer arms and a connecting section to join both the coiled sections. The connecting section could be position either above or below the outer arm. If the connecting section is positioned above the outer arm, the lower ends of the torsion spring may engage with the inner arm. If the connecting section is positioned below the inner arm, the upper ends of the torsion spring may engage with the outer arm. Also, in some embodiments the Z-stop pin could be eliminated and the lower ends of the first and second torsion springs may engage directly with the inner arm.

The foregoing description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. Therefore, the present embodiments should be considered illustrative and not restrictive and the invention is not to be limited to the details given herein but may be modified within the scope and equivalents of the appended claims. 

What is claimed is:
 1. A switchable roller finger follower comprising; an outer arm; an inner arm rotatably connected to the outer arm; a first torsion spring positioned at a mid-arm location on a first side of the outer arm; and a second torsion spring positioned at a mid-arm location on a second side of the outer arm, the second side being opposite the first side.
 2. The switchable roller finger follower as recited in claim 1 wherein the inner arm is rotatably connected to the outer arm by a pivot shaft.
 3. The switchable roller finger follower as recited in claim 1 further comprising a third torsion spring.
 4. The switchable roller finger follower as recited in claim 3 wherein the third torsion spring is situated around a pivot shaft.
 5. The switchable roller finger follower as recited in claim 1 wherein the outer arm has two bosses that extend outward from the outer arm body at a mid-arm position and one of the two bosses is located on one side of the outer arm body and the other of the two bosses is located on a second, opposed side of the outer arm body.
 6. The switchable roller finger follower as recited in claim 5 wherein a coil of the first torsion spring is supported by one of the two bosses and a coil of the second torsion spring is supported by the second of the two bosses.
 7. The switchable roller finger follower as recited in claim 1 wherein the inner arm has two holes situated on opposite sides of the inner arm and the two holes are configured to accept a Z-stop pin.
 8. The switchable roller finger follower as recited in claim 7 wherein an upper end of the first torsion spring engages with a top surface of the outer arm and a lower end of the first torsion spring engages with the Z-stop pin.
 9. The switchable roller finger follower as recited in claim 8 wherein an upper end of the second torsion spring engages with a top surface of the outer arm and a lower end of the second torsion spring engages with the Z-stop pin.
 10. A switchable roller finger follower comprising; an outer arm; an inner arm rotatably connected to the outer arm; and a torsion spring, wherein the torsion spring has a first coiled section positioned at a mid-arm location on a first side of the outer arm and a second coiled section positioned at a mid-arm location on a second side of the outer arm, the second side being opposite the first side.
 11. The switchable roller finger follower as recited in claim 10 wherein the inner arm is rotatably connected to the outer arm by a pivot shaft.
 12. The switchable roller finger follower as recited in claim 10 further comprising a third torsion spring.
 13. The switchable roller finger follower as recited in claim 12 wherein the third torsion spring is situated around a pivot shaft.
 14. The switchable roller finger follower as recited in claim 10 wherein the outer arm has two bosses that extend outward from the outer arm body at a mid-arm position and one of the two bosses is located on one side of the outer arm body and the other of the two bosses is located on a second, opposed side of the outer arm body.
 15. The switchable roller finger follower as recited in claim 14 wherein the first coil of the torsion spring is supported by one of the two bosses and the second coil of the torsion spring is supported by the other of the two bosses.
 16. The switchable roller finger follower as recited in claim 10 wherein the inner arm has two holes situated on opposite sides of the inner arm and the two holes are configured to accept a Z-stop pin.
 17. The switchable roller finger follower as recited in claim 16 wherein a connecting section of the torsion spring located between the first coil and the second coil engages with a top surface of the outer arm and a lower end of the torsion spring engages with the Z-stop pin.
 18. The switchable roller finger follower as recited in claim 16 wherein a connection section of the torsion spring located between the first coil and the second coil engages with the inner arm and an upper end of the torsion spring engages with the upper arm.
 19. A switchable roller finger follower comprising; an outer arm; an inner arm rotatably connected to the outer arm; and a torsion spring; wherein the widest portion of the switchable roller finger follower is located in a mid-arm location.
 20. The switchable roller finger follower as recited in claim 19 wherein the switchable roller finger follower is for a Type II valve train. 